1. Field of the Invention
The present invention relates to a natural-draft cooling tower having a plurality of preferably roof-shaped heat exchange elements for condensing the turbine exhaust steam from a power plant. A portion of the heat exchange elements are connected to operate as condensers, and another portion of the heat exchange elements are connected to operate as dephlegmators, reflux condensers or fractionating columns, with the latter being disposed downstream of the heat exchange elements that are connected to operate as condensers when viewed in the direction of flow of the steam.
2. Description of the Prior Art
So-called natural-draft dry cooling towers are known that have heat exchange elements through which flows the cooling water of a closed water circuit; the cooling water effects the condensation of the turbine exhaust steam via indirect heat exchange in the condenser. In addition to this indirect system, a direct system is known where the steam is condensed directly in the heat exchange elements of the natural-draft cooling tower. In contrast to the indirect system, this direct system has the advantage of having a greater efficiency due to a greater temperature difference of approximately 2.degree.. With one known configuration of a natural-draft cooling tower of this type, one portion of the heat exchange elements are connected to operate as condensers, and another portion are connected to operate as dephlegmators, reflux condensers or fractionating columns, with the latter being disposed downstream, when viewed in the direction of flow of the steam, from the heat exchange elements which are connected to operate as condensers.
In order with the natural-draft cooling towers of the initially mentioned type to be able to assure a complete condensation of the turbine exhaust steam, the residual condensation must take place in the heat exchange elements that are connected to operate as dephlegmators. At the same time, one must guarantee that the inert gases are completely withdrawn from these heat exchange elements that are connected as dephlegmators. In order to accomplish this, it is important that the heat exchange elements operating as dephlegmators be supplied with a sufficient quantity of cooling air under all load and weather conditions. This is particularly difficult under unfavorable weather conditions, such as strong cross winds and an inversion, i.e., where warm air flows downwardly from above.
An object of the present invention is to improve a natural-draft cooling tower of the aforementioned general type for direct condensation of the turbine exhaust steam in such a way that a complete condensation of the turbine exhaust steam, with residual condensation in the heat exchange elements that are connected to operate as dephlegmators respectively reflux condensers, is effected over the entire range of capacity, even under unfavorable weather conditions.